1. Field of the Invention
This invention relates to the cementing of casing in oil and gas wells by use of cementing plugs. More specifically, the invention relates to the injection of cementing plugs into casing which is hung in a well prior to the cementing operation, and to displacement of cement from the casing after the cementing process has been completed. The cementing plug container assembly of this invention is designed to release a bottom cementing plug as an interface between the drilling fluid and the cement. The bottom cementing plug wipes the drilling fluid from the walls of the casing ahead of the cement slurry, reducing dilution. At completion of mixing of the cement, the cementing plug container drops a top cementing plug on command. The function of this plug is to follow cement and prevent contamination or channeling with the drilling fluid, or fluid used to displace the cement. The cementing plug container injects the bottom and top cementing plugs from the assembly housing into the casing at specified time intervals by operation of pneumatically controlled air cylinders and plug-release mechanisms cooperating with the air cylinders. The apparatus of this invention is further characterized by a plug pass indicator which positively indicates when a plug or plugs have passed from the interior of the cementing plug container assembly housing through the bore of the housing. The cementing plug container assembly is specifically designed to quickly, efficiently and inexpensively inject one or more cementing plugs into a length of casing in an oil or gas well before and after the casing cementing operation to minimize the time and cost of cementing the casing in the well and maximize safety during the cementing operation.
2. Description of the Prior Art
Oil and gas well cementing operations have long been achieved by the use of a cementing plug container assembly which is typically designed to contain a single cementing plug for injection into the casing of the well prior to injecting cement into the casing and to displace the cement after cement is forced through it to cement the casing in the well. In most prior art operations a first plug is initially inserted in the cementing plug container assembly by removing the dome, or top of the assembly, placing the plug in the assembly housing and then replacing the dome. After the loading operation is completed the plug is forced downwardly from the cementing plug container and through the casing by pumping cement into the casing on top of the plug, and the cement is forced through the casing and upwardly around the outside wall of the casing in the annulus between the well bore and the casing to secure the casing in position in the well. Subsequently, the dome is again removed and a second cementing plug is placed in the assembly housing and forced through the casing to clear the casing of residual cement. In some operations it may not be necessary to use a bottom cementing plug, and under these conditions a single top cementing plug is used.
It will be recognized by those skilled in the art that this procedure of removing the dome, placing cementing plugs inside the cementing plug container and subsequently replacing the dome in the sequence described above is expensive, constitutes a safey hazard, and is time-consuming. Accordingly, this operation adds time and expense to the cost of cementing and completing wells in oil and gas field operations, and has been known to create accidents. Furthermore, it is sometimes difficult to determine whether or not the plug or plugs have actually been forced from the cementing plug container into the casing, since no positive indicating mechanism is generally available to make this determination. Accordingly, it is frequently necessary to remove the dome from the assembly housing in order to be sure that each cementing plug has been forced from the cementing plug container assembly and into the casing.
Accordingly, it is an object of this invention to provide a new, improved and safer cementing plug container assembly which is characterized by at least one plug release mechanism which may be automatic in function, and serves to release one or more plugs in the assembly for injection into the well casing in a positive and efficient manner without the necessity of removing the dome from the assembly.
Another object of this invention is to provide a cementing plug container which is characterized by a plug pass indicator positioned beneath the plug release mechanism and having an internal wheel which is contacted by the cementing plug or plugs as they pass sequentially through the housing to positively indicate when the plugs have passed from the housing and through the cementing plug container assembly bore.
Yet another object of the invention is to provide a new and improved cementing plug container which is equipped with a plug release mechanism for supporting and releasing one or more cementing plugs, which mechanism is characterized by a separate air cylinder and cooperating release assembly or mechanism for releasing each plug in a specified and controlled sequence by pneumatic extension of the air cylinder piston; and a plug pass indicator device which is positioned beneath the plug release mechanism or mechanisms, and includes a star wheel rotatably disposed in the interior of the assembly housing for engagement with the cementing plug or plugs as they pass through the housing bore, and rotation responsive to this engagement to initiate movement of an indicator gear rack located externally of the cementing plug container assembly bore in order to positively indicate when a cementing plug has moved from the interior of the housing and through the bore of the housing.
A still further object of this invention is to provide a new and improved plug release mechanism for supporting and releasing one or more cementing plugs in a cementing plug container apparatus for cementing casing in oil and gas wells, which release mechanism includes a support arm carrying the plug and attached to a release shaft, which is in turn carried by a release cam for maintaining the release arm in supporting configuration; the release cam further cooperating with an air cylinder designed to permit downward rotation of the release arm by extension of the air cylinder piston and allow the cementing plug to drop from the upper interior portion of the assembly housing into the bore of the housing for injection into the casing.
Another object of the invention is to provide a positive and efficient indicator mechanism for determining when one or more cementing plugs have moved from the upper segment of the cementing plug container housing and through the bore of the housing, which indicator includes a wheel rotatably positioned in the bore of the housing and having teeth which extend into the path of the plug or plugs, and a shaft carrying the wheel and extending through the housing to cooperate with a rack which is slidably mounted on the exterior of the housing and is movable upon rotation of the wheel responsive to contact between the wheel and a falling cementing plug in the cementing plug container assembly housing bore.